Types of Plant Tissues
In plants, there are two kinds of tissues viz. Meristematic tissues and Permanent Tissues.
Meristematic Issue
The Meristematic tissues are divisible and cells in these tissues retain the power of division, so that plant keeps growing. These tissues are found in the regions of plant growth such as apical tissues, buds, nodes, side of branches etc.
Apical Dominance by Meristematic Tissues
Apical Dominance means that in plants, one Meristem {regions of growth / Meristematic tissues} inhibits the growth of other Meristems. The result of this is that a plant has one clearly defined main trunk. The tip of the main trunk bears the dominant Meristem and grows rapidly. It is not shadowed by branches. If the dominant Meristem is cut off, one or more branch tips will assume dominance. The branch will start growing faster and the new growth will be horizontal. To get a bushy growth, the tip of the main trunk is removed. This mechanism is based upon Auxin hormone which is produced in the apical Meristem and transported towards the roots in the cambium.
Permanent Tissue
Permanent tissues are formed by the cells which lose the power of division. Cells in permanent tissue are either living or dead. These cells have thick cell walls. These tissues are either simple {made of similar types of cells} or complex {made of different types of cells, working as single unit}.
Simple Tissues
Simple permanent tissues are of three kinds viz. parenchyma, collenchyma and sclerenchyma. Parenchyma tissues are the most vital parts and centers of important physiological functions such as respiration, photosynthesis, storage, secretion etc. These tissues help in growth and repair, wound healing, formation of adventitious roots. In succulent plants (Succulent plants are water-retaining plants adapted to arid climate or soil conditions, such as Carissa carandas or Karonda), these tissues store water; while in aquatic plants they store air. The collenchyma tissue also has living cells but these cells are with thick cell walls and provide tensile strength. It works both as vital and mechanical tissues. Sclerenchyma is made of dead cells and it works as mechanical tissues.
Complex Tissues
In plants, the complex tissues are Xylem and Phloem. Xylem (wood) conducts water and minerals from root to leaves and also provides mechanical strength. It remains at inner side in the root and in the form of wooden columns in stems as shown below:
Phloem or wood conducts the prepared food material from the leaves to the storage organs and growing organs. Generally Phloem is found outside the vascular cambium, but in some plants it may be found inside the pith also in the form of intraxylary phloem.
Why plants die when bark is removed?
Here we note that when bark of a tree is removed in a circular fashion all around near its base, it gradually dries up and dies because roots are starved of energy. This is because removal of bark means removal of phloem and absence of phloem would block transport of soluble organic material made during photosynthesis in leaves to root of the plant.
Other Tissues in Plants
Plants also have secretory tissues such as water stomata or hydathodes. The water stomata release water via a process called guttation in aquatic plants. Pistia (also called water cabbage / water lettuce) is one such aquatic plant that has water stomata. Further, some plants are insectivorous (example Nepenthes, Pitcher plant) which have secretory tissues that release some poisonous material to kill the insects. Further, in Rubber plants (Ficus elastica and Havea brasiliensis), the laticiferous tissue secretes latex, which is dried and processed to produce natural rubber.
